1. Field of the Invention
The present invention relates to an apparatus that extracts line-art vector information from a thinned binary image.
2. Description of the Related Art
There has been a growing demand for paperless environments and existing hardcopy image data are often converted to digital formats and reused in these days. In order to reuse image data, the image data is binarized, and then the binary image data is converted to vector data by using a vectorization technique. Then the vector data is used in applications such as CAD software. Various techniques concerning vectorization of image data have been developed.
Japanese Patent No. 3026592 discloses an image processing apparatus that extracts a group of independent vectors corresponding to line components of a binary graphic or line drawing which is a set of independent lines and closed curves that connect endpoints of lines and intersection points of lines constituting the binary graphic or line drawing from a thinned binary image in a single raster scan. According to Japanese Patent No. 3026592, all contours in the thinned binary image can be extracted in only one series of raster scanning and, since image memory for storing the whole image data is not required, the memory space can be saved. In addition, by extracting contours of edges of pixels of an input image, instead of center positions of the pixels, the contours can have a significant width for a single-pixel-wide thin line. Furthermore, it is described that not only a contour of a connected pixel region in an original image in which pixels are connected in four directions but also a contour of a pixel region in which pixels are connected in eight directions can be extracted. Japanese Patent Laid-Open No. 2005-346137 discloses a processing method and apparatus that provide function approximation of contour information representing a high-quality scaled-up or scaled-down image with a less amount of data by approximating not only straight lines in contour information in a binary image but also two- or three-dimensional Bezier curves.
Various techniques have also been developed for vectorizing such binary images, especially thinned binary images (line-art images). Expectations have grown for development of a thinning technique for thinning a line-art image consisting of boundaries of regions of the same color that constitute a clip art, for example.